The calendar says spring, but the Santa Ana-powered heat wave roiling the Southland this week and stirring up wildfires, health alerts and rattlesnakes seems more like weather typically reserved for late summer and early fall.

Climatologists warned that the unseasonably hot, potentially record-breaking days ahead are an omen of what could be an unusually hot summer not only here but across a large swath of the nation.

This week alone warnings have been issued for high winds, triple-digit temps and aroused rattlesnakes. North and south of Los Angeles on Tuesday the unseasonable heat fueled wildfires that blackened tinder-dry hillsides and threatened more than 20,000 homes in San Diego and Santa Barbara counties.

High pressure

The cause of it all is a large high-pressure system stretching from Oregon to Mexico. Coupled with Santa Ana winds out of the Northeast, the conditions pushed valley temperatures into the upper 90s and lower 100s. And, there was little relief on the coast.

By the weekend, the high pressure system and winds will lighten up and give way to more seasonable temperatures in the upper 70s and 80s. As short-lived as the heat wave may be, it’s an early indicator that supports a previous forecast by the Climate Prediction Center that suggests that May through July will be warmer than usual, along with a wide swath of the U.S.

The traditional “May Gray/June Gloom” period resulting from onshore flow could be nonexistent this summer, Patzert said.

Patzert, who studies Earth’s climate by monitoring JPL satellites, called the shift in weather patterns “ominous” and “worrisome.”

All the more so as it comes on the heels of a drier-than-normal winter and in the midst of an historic drought.

“This is insult to injury, because what little moisture that’s in the air is going to be evaporated through Thursday,” Patzert said.

Even at the beach the air was stifling, with the temperature reaching 90 degrees by 10 a.m. along the water in Redondo Beach.

The sand was surprisingly empty, with the majority of those down at the beach actually in the water.

She came to the Esplanade to walk her golden doodle, Krishna, who has a long, shaggy coat of curly hair, hoping to get some relief near the water.

Kleven said she was struggling to keep Krishna cool.

“Usually there’s at least a breeze down here,” she said. “It’s ridiculous.”

San Diego fire

In San Diego, wildfires pushed by gusty winds chewed through canyons parched by California’s drought, prompting evacuation orders for more than 20,000 homes on the outskirts of San Diego and another 1,200 homes and businesses in Santa Barbara County 250 miles to the north.

No homes were reported damaged in either fire, but hundreds were considered threatened. The rugged terrain and unseasonably warm temperatures made firefighting even more difficult.

The flames that erupted in the fire-prone Rancho Bernardo area of San Diego quickly grew to 700 acres, driven by hot, dry Santa Ana winds that whipped through areas dotted by hilltop estates and pricey new housing tracts.

Black and gray smoke billowed over the area, filled with whirling ash and embers that created small spot fires. Flames crept within yards of some homes before firefighters doused them.

Mountain cool

One of the few spots that remained relatively cool was Big Bear in the San Bernardino Mountains. Temperatures are expected to hover in the 70s during the day and drop into the 50s at night.

It’s going to be a shot in the arm for business.

“Big Bear is going to be the cool spot to get away,” said Dan McKernan, spokesman for Big Bear Visitors Bureau, formerly Big Bear Lake Resort Association. “You see people retreating to where they need to go, which is the place to cool off. When the heat rises, our business does do better.”

Record heat

Wednesday and Thursday L.A. will flirt with, and possibly break, record highs downtown as well as in Long Beach, Burbank and Woodland Hills. At 93, record temperatures were set Tuesday in Oxnard and Camarillo in Ventura County, according to Stuart Seto, National Weather Service specialist.

In the Inland Empire, the mercury could rise as high as 104 degrees on Thursday. It’s going to be even hotter in other areas such as Needles, where triple-digit temperatures will linger at least through Saturday.

Preparations

The Los Angeles Emergency Management Department announced that city libraries will be open until 8 p.m. through Thursday and 5:30 p.m. on Friday for reprieve from the heat. Some recreation and park facilities in Canoga Park, Panorama City, North Hollywood, Lake View Terrace, Sunland and Sherman Oaks will be open through Thursday from 10 a.m. to 9 p.m.

Cooling centers in the rest of Los Angeles County have been established in communities from Lancaster to San Pedro and from La Verne to Santa Monica.

Late Tuesday as officials sought the upper hand against the wildfires in San Diego and Santa Barbara, Los Angeles City Fire Department announced the mobilization of five engine companies in fire-prone areas in the San Fernando Valley: Hollywood Hills, Santa Monica Mountains, Sunland-Tujunga, Porter Ranch and Woodland Hills. Twenty-one extra fire engines, staffed by firefighters who originally had the day off, and 15 extra brush patrols will be out in force.

“Just in case there’s something, we’ll have a quick attack on it,” LAFD spokesman Cody Weireter said. “Every day is a concern for us, not just with brush fires or grass fires but also medical emergencies. We really want to push the public to stay hydrated and (refrain from) doing any strenuous activities outside.”

Los Angeles County Fire Department has staffed 100 additional firefighters to additional posts throughout the county, as well as pre-positioned a strike team in Agoura Hills, a task force in Malibu, and a Cal Fire strike team has been assigned to the Santa Clarita Valley, inspector Tony Akins said.

Cal Fire’s San Bernardino unit is also ready for high winds and heat, bringing in a Northern California strike team of about 21 personnel, as well as hand crews, down to San Bernardino.

“They’re pre-positioned here and are centrally located and ready for a response,” said Debbie Chapman, Cal Fire spokeswoman.

Staff writers Carley Dryden and Melissa Pinion-Whitt and The Associated Press contributed to this report.

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